Conformational assignments and a nitrogen inversion process in some 3-acyloxy-1,3-oxazinanes by NMR and X-ray analysis

The stereochemistry of the preferred conformers of several 3-acyldxy-1,3-ox azinanes has been established by NMR spectroscopy. A strong anomeric effect stabilizes the conformation having an equatorial orientation of the lone p air on nitrogen. A nitrogen inversion process was found to be the rate-limi ting process in the conformational equilibria. The range of Delta G double dagger values was found to be 60-71 kJ mol(-1). Solid state structures as d etermined by X-ray diffraction confirm the findings of the NMR study.